Field of the Invention
The present invention relaters to a humidification device and an image forming apparatus.
Description of the Related Art
An electrophotographic image forming apparatus, such as a copier, a printer, a facsimile machine, and a multifunction peripheral having the functions of these apparatuses, has such a problem that a sheet loses moisture in a thermal fixing step, and thus curls or deforms into a wave form.
Japanese Patent Application Laid-Open No. 2007-58026 discusses a technique of providing water to a sheet after performing fixing processing, as one technique to solve the problem described above. More specifically, an image forming apparatus discussed in Japanese Patent Application Laid-Open No. 2007-58026 includes a pair of porous rollers that conveys a sheet and forms a nip portion, and a water supply roller that comes into contact with the porous roller and supplies water.
This configuration has a problem that, due to the difference in an interval between sheets, the first sheet is provided with a larger amount of water than the second sheet and after. To address this problem, the image forming apparatus discussed in Japanese Patent Application Laid-Open No. 2007-58026 performs a control so that pressure contact between the pair of porous rollers is released in an idling state where no image forming is performed.
However, the configuration discussed in Japanese Patent Application Laid-Open No. 2007-58026, may cause uneven distribution (unevenness) of liquid on a surface of the water-supply roller upon returning from the idling state where no image forming is performed. The uneven distribution is especially likely to occur between portions, on the surface of the water-supply roller, immersed and not immersed in a water-supply container. When a recording medium, which has entered a humidification device, is humidified in the state described above, the recording medium is unevenly humidified in a portion from the leading edge to the trailing edge.
To reduce the uneven distribution of liquid on the surface of the water-supply roller, the water-supply roller may be rotated before the recording medium reaches a nip formed by the pair of porous rollers. However, when the water-supply roller is rotated before the recording medium reaches the nip formed by the pair of porous rollers, the liquid supplied to the pair of porous rollers from the water-supply roller is accumulated in the nip formed by the pair of porous rollers instead of being provided to the recording medium. Thus, there is a problem that when the recording medium is conveyed to the nip formed by the pair of porous rollers in this state, an excessive amount of water is provided to the leading edge side of the recording medium. This problem also occurs when a pair of solid rollers is used instead of a pair of porous rollers.